Various sensor devices and methods have been utilized to detect target molecules or particulates. Certain sensors involve detection or measurement of biological elements utilizing antibody-antigen interactions. While such sensors may have high specificity, they may have a number of limitations including inadequate sensitivity and the need to utilize labels.
More particularly, certain known sensors require attachment of a label to molecules that are to be detected. This requires prior knowledge of the presence of the target molecule. As a result, known label-based sensor systems are not suitable for blind or label-free detection. Further, use of labels may require additional data processing and ensemble averaging of large numbers of cells. Such processing may confuse or dull recorded responses.
Certain sensors are highly sensitive and capable of detecting a small number of molecules. For example, two known single molecule detection methods include surface enhanced raman spectroscopy (SERS) and total internal reflection fluorescence microscopy (TIRF). However, labels are needed to detect single molecules using these methods. More particularly, a gold surface is used in SERS to amplify a signal corresponding to a single labeled molecule, and with TIRF, a fluorescent label is excited and detected using a single photon camera. Such methods, however, may not be suitable for detecting single molecules in the absence of these labels.
Several sensor devices have been proposed for label-free detection including fiber optic waveguides, nanowires, nanoparticle probes, biochips, mechanical cantilevers and micro-sphere resonators. Examples of such known devices are described in U.S. Pat. No. 4,071,753 to Fulenwider et al., U.S. Pat. No. 4,419,895 to Fuller and U.S. Pat. No. 6,583,399 to Painter et al. While certain known devices may provide label-free detection capabilities, they have a number of limitations and may not be suitable for various applications and may present integration challenges.
Certain known sensors having functionalized outer surfaces for purposes of selective sensing or detection applications. Such sensors, however, may utilize surface functionalization elements and methods that involve weak bonds that are unable to retain target molecules to the functionalized surface, thereby reducing the effectiveness of the sensor. Other known sensors may have stronger bonds but are silane-based, do not form uniform monolayers, lack high binding efficiency, have limited stability in air or an ambient environment, must be stored in a buffer solution and/or have limited shelf lives and storage restrictions.